1. Field of the Invention
The invention relates to superhard polycrystalline material elements for wear, cutting, drawing, and other applications where engineered superhard surfaces are needed. The invention particularly relates to polycrystalline diamond and polycrystalline diamond-like (collectively called PCD) elements with greatly improved wear resistance and methods of manufacturing them.
2. Description of Related Art
Polycrystalline diamond and polycrystalline diamond-like elements are known, for the purposes of this specification, as PCD elements. PCD elements are formed from carbon based materials with exceptionally short inter-atomic distances between neighboring atoms. One type of polycrystalline diamond-like material is known as carbonitride (CN) described in U.S. Pat. No. 5,776,615. Another, more commonly used form of PCD is described in more detail below. In general, PCD elements are formed from a mix of materials processed under high-temperature and high-pressure into a polycrystalline matrix of inter-bonded superhard carbon based crystals. A common trait of PCD elements is the use of catalyzing materials during their formation, the residue from which, often imposes a limit upon the maximum useful operating temperature of the element while in service.
A well known, manufactured form of PCD element is a two-layer or multi-layer PCD element where a facing table of polycrystalline diamond is integrally bonded to a substrate of less hard material, such as tungsten carbide. The PCD element may be in the form of a circular or part-circular tablet, or may be formed into other shapes, suitable for applications such as hollow dies, heat sinks, friction bearings, valve surfaces, indentors, tool mandrels, etc. PCD elements of this type may be used in almost any application where a hard wear and erosion resistant material is required. The substrate of the PCD element may be brazed to a carrier, often also of cemented tungsten carbide. This is a common configuration for PCDxe2x80x9cs used as cutting elements, for example in fixed cutter or rolling cutter earth boring bits when received in a socket of the drill bit, or when fixed to a post in a machine tool for machining. These PCD elements are typically called PDCxe2x80x9cs.
Another form of PCD element is a unitary PCD element without an integral substrate where a table of polycrystalline diamond is fixed to a tool or wear surface by mechanical means or a bonding process. These PCD elements differ from those above in that diamond particles are present throughout the element. These PCD elements may be held in place mechanically, they may be embedded within a larger PCD element that has a substrate, or, alternately, they may be fabricated with a metallic layer which may be bonded with a brazing or welding process. A plurality of these elements may be made from a single PCD, as shown, for example, in U.S. Pat. Nos. 4,481,016 and 4,525,179 herein incorporated by reference for all they disclose.
PCD elements are most often formed by sintering diamond powder with a suitable binder-catalyzing material in a high-pressure, high-temperature press. One particular method of forming this polycrystalline diamond is disclosed in U.S. Pat. No. 3,141,746 herein incorporated by reference for all it discloses. In one common process for manufacturing PCD elements, diamond powder is applied to the surface of a preformed tungsten carbide substrate incorporating cobalt. The assembly is then subjected to very high temperature and pressure in a press. During this process, cobalt migrates from the substrate into the diamond layer and acts as a binder-catalyzing material, causing the diamond particles to bond to one another with diamond-to-diamond bonding, and also causing the diamond layer to bond to the substrate.
The completed PCD element has at least one matrix of diamond crystals bonded to each other with many interstices containing a binder-catalyzing material metal as described above. The diamond crystals comprise a first continuous matrix of diamond, and the interstices form a second continuous matrix of interstices containing the binder-catalyzing material. In addition, there are necessarily a relatively few areas where the diamond to diamond growth has encapsulated some of the binder-catalyzing material. These xe2x80x9cislandsxe2x80x9d are not part of the continuous interstitial matrix of binder-catalyzing material.
In one common form, the diamond element constitutes 85% to 95% by volume and the binder-catalyzing material the other 5% to 15%. Such an element may be subject to thermal degradation due to differential thermal expansion between the interstitial cobalt binder-catalyzing material and diamond matrix beginning at temperatures of about 400 degrees C. Upon sufficient expansion the diamond-to-diamond bonding may be ruptured and cracks and chips may occur.
Also in polycrystalline diamond, the presence of the binder-catalyzing material in the interstitial regions adhering to the diamond crystals of the diamond matrix leads to another form of thermal degradation. Due to the presence of the binder-catalyzing material, the diamond is caused to graphitize as temperature increases, typically limiting the operation temperature to about 750 degrees C.
Although cobalt is most commonly used as the binder-catalyzing material, any group VIII element, including cobalt, nickel, iron, and alloys thereof, may be employed.
To reduce thermal degradation, so-called xe2x80x9cthermally stablexe2x80x9d polycrystalline diamond components have been produced as preform PCD elements for cutting and/or wear resistant elements, as disclosed in U.S. Pat. No. 4,224,380 herein incorporated by reference for all it discloses. In one type of thermally stable PCD element the cobalt or other binder-catalyzing material in conventional polycrystalline diamond is leached out from the continuous interstitial matrix after formation. While this may increase the temperature resistance of the diamond to about 1200 degrees C., the leaching process also removes the cemented carbide substrate. In addition, because there is no integral substrate or other bondable surface, there are severe difficulties in mounting such material for use in operation.
The fabrication methods for this xe2x80x9cthermally stablexe2x80x9d PCD element typically produce relatively low diamond densities, of the order of 80% or less. This low diamond density enables a thorough leaching process, but the resulting finished part is typically relatively weak in impact strength.
In an alternative form of thermally stable polycrystalline diamond, silicon is used as the catalyzing material. The process for making polycrystalline diamond with a silicon catalyzing material is quite similar to that described above, except that at synthesis temperatures and pressures, most of the silicon is reacted to form silicon carbide, which is not an effective catalyzing material. The thermal resistance is somewhat improved, but thermal degradation still occurs due to some residual silicon remaining, generally uniformly distributed in the interstices of the interstitial matrix. Again, there are mounting problems with this type of PCD element because there is no bondable surface.
More recently, a further type of PCD has become available in which carbonates, such as powdery carbonates of Mg, Ca, Sr, and Ba are used as the binder-catalyzing material when sintering the diamond powder. PCD of this type typically has greater wear-resistance and hardness than the previous types of PCD elements. However, the material is difficult to produce on a commercial scale since much higher pressures are required for sintering than is the case with conventional and thermally stable polycrystalline diamond. One result of this is that the bodies of polycrystalline diamond produced by this method are smaller than conventional polycrystalline diamond elements. Again, thermal degradation may still occur due to the residual binder-catalyzing material remaining in the interstices. Again, because there is no integral substrate or other bondable surface, there are difficulties in mounting this material to a working surface.
Efforts to combine thermally stable PCDxe2x80x9cs with mounting systems to put their improved temperature stability to use have not been as successful as hoped due to their low impact strength. For example, various ways of mounting multiple PCD elements are shown in U.S. Pat. Nos. 4,726,718; 5,199,832; 5,025,684; 5,238,074; 6,009,963 herein incorporated by reference for all they disclose. Although many of these designs have had commercial success, the designs have not been particularly successful in combining high wear and/or abrasion resistance while maintaining the level of toughness attainable in non-thermally stable PCD.
Other types of diamond or diamond like coatings for surfaces are disclosed in U.S. Pat. Nos. 4,976,324; 5,213,248; 5,337,844; 5,379,853; 5,496,638; 5,523,121; 5,624,068 all herein incorporated by reference for all they disclose. Similar coatings are also disclosed in GB Patent Publication No. 2,268,768, PCT Publication No. 96/34,131, and EPC Publications 500,253; 787,820; 860,515 for highly loaded tool surfaces. In these publications, diamond and/or diamond like coatings are shown applied on surfaces for wear and/or erosion resistance.
In many of the above applications physical vapor deposition (PVD) and/or vapor deposition (CVD) processes are used to apply the diamond or diamond like coating. PVD and CVD diamond coating processes are well known and are described for example in U.S. Pat. Nos. 5,439,492; 4,707,384; 4,645,977; 4,504,519; 4,486,286 all herein incorporated by reference.
PVD and/or CVD processes to coat surfaces with diamond or diamond like coatings may be used, for example, to provide a closely packed set of epitaxially oriented crystals of diamond or other superhard crystals on a surface. Although these materials have very high diamond densities because they are so closely packed, there is no significant amount of diamond to diamond bonding between adjacent crystals, making them quite weak overall, and subject to fracture when high shear loads are applied. The result is that although these coatings have very high diamond densities, they tend to be mechanically weak, causing very poor impact toughness and abrasion resistance when used in highly loaded applications such as with cutting elements, bearing devices, wear elements, and dies.
Some attempts have been made to improve the toughness and wear resistance of these diamond or diamond like coatings by application to a tungsten carbide substrate and subsequently processing in a high-pressure, high-temperature environment as described in U.S. Pat. Nos. 5,264,283; 5,496,638; 5,624,068 herein incorporated by reference for all they contain. Although this type of processing may improve the wear resistance of the diamond layer, the abrupt transition between the high-density diamond layer and the substrate make the diamond layer susceptible to wholesale fracture at the interface at very low strains. This translates to very poor toughness and impact resistance in service.
When PCD elements made with a cobalt or other group VIII metal binder-catalyzing material were used against each other as bearing materials, it was found that the coefficient of friction tended to increase with use. As described in European Patent specification number 617,207, it was found that removal (by use of a hydrochloric acid wipe) of the cobalt-rich tribofilm which tended to build up in service from the surface of the PCD bearing element, tended to mitigate this problem. Apparently, during operation, some of the cobalt from the PCD at the surface migrates to the load area of the bearing, causing increased friction when two PCD elements act against each other as bearings. It is now believed that the source of this cobalt may be a residual by-product of the finishing process of the bearing elements, as the acid wipe remedy cannot effectively remove the cobalt to any significant depth below the surface.
Because the cobalt is removed only from the surface of the PCD, there is no effective change in the temperatures at which thermal degradation occurs in these bearing elements. Therefore the deleterious effects of the binder-catalyzing material remain, and thermal degradation of the diamond layer due to the presence of the catalyzing material still occurs.
The present invention provides a superhard polycrystalline diamond or diamond-like element with greatly improved resistance to thermal degradation without loss of impact strength. Collectively called PCD elements for the purposes of this specification, these elements are formed with a binder-catalyzing material in a high-temperature, high-pressure process. The PCD element has a plurality of partially bonded diamond or diamond-like crystals forming at least one continuous diamond matrix, and the interstices among the diamond crystals forming at least one continuous interstitial matrix containing a catalyzing material. The element has a working surface and a body, where a portion of the interstitial matrix in the body adjacent to the working surface is substantially free of the catalyzing material, and the remaining interstitial matrix contains the catalyzing material.
A portion of the working surface on the body of the PCD element may be post-processed so that the interstices among the superhard crystals are substantially free of the catalyzing material. The working surface that is substantially free of the catalyzing material is not subject to the thermal degradation encountered in the other areas of the working surface, resulting in improved resistance to thermal degradation. In cutting elements, the processed working surface may be a portion of the facing table of the body, a portion of the peripheral surface of the body, or portions of all these surfaces.
In another embodiment, the catalyzing material is cobalt or other iron group metal, and the method of depleting the catalyzing material is to leach it from the interstices near the surface of a PCD element in an acid etching process. It is anticipated that the method of removing the catalyzing material from the surface may also be by electrical discharge, or other electrical or galvanic process, or by evaporation.
In another embodiment, the catalyzing material is subsequently removed from the working surface of a PCD element by combining it chemically with another material such that it no longer acts as a catalyzing material. In this method, a material may remain in the interstices among the diamond crystals, but that material no longer acts as a catalyzing material effectively removing or depleting the catalyzing material.
In still another embodiment, the catalyzing material is removed by causing it to transform into a material that no longer acts as a catalyzing material. This may be accomplished by a crystal structure change, mechanical xe2x80x9cworkingxe2x80x9d, thermal treatment or other treatment methods. This method may apply to non-metallic or non-reactive catalyzing materials. Again, a material may remain in the interstices among the superhard material crystals, but that material no longer acts as a catalyzing material effectively removing or depleting the catalyzing material.
Disclosed is an element comprising a plurality of partially bonded diamond crystals, a catalyzing material, an interstitial matrix, and a body with a working surface. The interstitial matrix in the body adjacent to the working surface is substantially free of the catalyzing material, and the remaining interstitial matrix contains the catalyzing material.
Similarly, a PCD element is disclosed having a catalyzing material, an interstitial matrix, and a body with a working surface. The interstitial matrix in the body adjacent to the working surface is substantially free of the catalyzing material, and the remaining interstitial matrix contains the catalyzing material.
Also, a PCD element is disclosed having a plurality of superhard crystals, a catalyzing material and a body with a working surface. In this element, a majority of the crystals in the body within at least a 0.1 mm depth from the working surface have a surface which is substantially free of the catalyzing material and the remaining crystals are contacting the catalyzing material.
Furthermore, a PCD element is disclosed having a body with a working surface. A first volume of the body remote from the working surface contains a catalyzing material, and a second volume of the body adjacent to the working surface is substantially free of the catalyzing material.
Also, an element is disclosed having a plurality of partially bonded diamond crystals, a catalyzing material, and a body with a working surface. The volume of the body adjacent the working surface has a substantially higher diamond density than elsewhere in the body, and the volume is substantially free of the catalyzing material.
Also, a PCD element is disclosed having a body with a working surface. The volume of the body adjacent to the working surface has a diamond density substantially higher than elsewhere in the body, and the volume is substantially free of a catalyzing material.
In addition, a preform cutting element is disclosed. The element has a facing table of a superhard polycrystalline material having a plurality of partially bonded superhard crystals, a plurality of interstitial regions among the superhard crystals and a catalyzing material. The facing table has a cutting surface and a body. The interstitial regions in at least a portion of the cutting surface are substantially free of the catalyzing material and the remainder of the interstitial regions contain the catalyzing material.
The PCD elements of the present invention may be used for wear, cutting, drawing, and other applications where engineered diamond surfaces are needed. Specific applications are as cutting elements in rotary drill bits of both the fixed cutter type and the rolling cutter type, as hollow dies, heat sinks, friction bearings, valve surfaces, indentors, tool mandrels, etc. The PCD element of the present invention may be used to machine abrasive wood products, ferrous and nonferrous materials and also very hard or abrasive engineering materials such as stone and asphalt and the like.